US3330932A

US3330932A - High frequency dielectric heating process and apparatus

Info

Publication number: US3330932A
Application number: US414602A
Authority: US
Inventors: Gros Chajim
Original assignee: Individual
Current assignee: Individual
Priority date: 1963-11-30
Filing date: 1963-11-30
Publication date: 1967-07-11
Anticipated expiration: 1984-07-11
Also published as: DE1540778A1; GB1042920A

Description

C. GROS July H, 1967 HIGH FREQUENCY DIELECTRIC HEATING PROCESS AND APPARATUS Filed Nov. 30, 1964 United States Patent 3,330,932 HIGH FREQUENCY DIELECTRIC HEATING PROCESS AND APPARATUS Chajim Gros, 39 Alexandra Road, London, England Filed Nov. 30, 1964, Ser. No. 414,602 Claims priority, application Great Britain, Nov. 30, 1963, 47,361/ 63 8 Claims. (Cl. 219-10.61)

ABSTRACT OF THE DISCLOSURE A high frequency heating process for supplying power across the whole width of a dielectric material during longitudinal movement of the material between electrodes in which one of the electrodes is divided with respect to the high frequency power into a plurality of parts in such a way that each part covers a portion of the material not covered by another part during its passage between the electrodes.

This invention relates to a high frequency dielectric heating process and apparatus.

One of the problems encountered in the operation of such processes is that it is normally necessary when an increase is made in the area of dielectric material to be heated to increase the area of the electrodes between which the dielectric material is placed and the power supplied to the electrodes to avoid amongst other things the generation of standing waves and to decrease the frequency of the source of the power. This results in an increase in the voltage stress across the dielectric material to achieve satisfactory heating and the consequent increase in the possibility of an electrical breakdown of the insulation between the electrodes.

The present invention provides a process and apparatus in which the possibility of an electrical breakdown in the insulation between the electrodes occurring is reduced and in which use may be made of a higher frequency source than would otherwise be possible. The term high frequency where used in this specification and claims is not limited, in its application to any one band of [frequencies but it may include for example frequencies in the very high and ultra high frequency bands.

The term dielectric heating where used in this specification and claims includes any form of heating in which heat is generated by placing a dielectric material in an alternating electric field.

According to the present invention there is provided a high-frequency dielectric heating process which includes the steps of supplying high frequency power from a source to two electrodes so that a high frequency electric field is set up between the electrodes, and passing a dielectric material in a longitudinal direction between the electrodes, the arrangement being such that one of the electrodes is effectively divided electrically with respect to the high frequency power into a plurality of parts arranged across the width of the material so that each part covers a portion of the material not covered by another part during the passage of the material between the electrodes whereby power from the source is developed as heat in the material across different portions of the width of the material each corresponding to a respective one of the said parts.

According to the present invention there is further provided high frequency dielectric heating apparatus including a first electrode, a second electrode arranged to hold a dielectric sheet material against the first electrode, means to cause relative movement between the material and the electrodes, a source of high frequency electrical power, and electrical connections between the source and the electrodes, the arrangement being such that in operation one of the electrodes is effectively divided electrically with respect to high frequency power from the source into a plurality of parts arranged across the width of the material so that each part covers a portion of the material not covered by another part, whereby power (from the source is developed as heat in the material across different portions of the width of the material each corresponding to a respective one of the said parts.

Embodiments of the invention will now be described with reference to the accompanying drawings which show,

In FIGURE 1 a plan view of an arrangment of roller electrodes,

In FIGURE 2 a diagrammatic end view of the roller electrodes shown in FIGURE 1,

In FIGURES 3, 4, 5 and 7 diagrammatic side elevations of roller electrode arrangements together with their circuit connections, and

In FIGURE 6 a diagrammatic plan view of a roller electrode arrangement together with its circuit connections.

Referring to FIGURES 1 and 2 there is shown a first electrode which consists of a metal roller 1 having a raised pattern 2 on its surface. Arranged on an are about the roller 1 there is a second electrode composed of three metal pressure rollers 3, 4 and 5. These pressure rollers are carried on shafts 6, 7 and 8 of insulating material. The shafts are of smaller diameter than the pressure rollers so that when a sheet of insulating material is passed between the roller 1 and the rollers 3, 4 and 5 it is pressed against the pattern 2 over only a third of its width by each pressure roller. In operation the roller 1 which forms one electrode of a dielectric heating apparatus is connected to one terminal of a source of high frequency heating power. Another terminal of the source is connected to one of the pressure rollers, for example to roller 3. The connections are made from the source by the normal type of roller contact, and are not illustrated in the figures. A second source is connected between the roller 1 and the roller 4, and a third source is connected between the roller 1 and the roller 5. The sources may all be completely independent generators or they may be separate secondary windings on the output of a single generator.

In operation thermoplastic dielectric material is fed between the rollers 3, 4, 5, and roller 2 which is driven. Power from the sources at a frequency which matches the load provided by the dielectric material is fed to the electrodes and the dielectric material is heated to such a temperature that the pattern which is imprinted or embossed into it by the roller 1 remains in the material upon cooling.

From the above description it can be seen that the second electrode is divided electrically with respect to the high frequency power into a plurality of parts formed by the rollers 3, 4, and 5 so that heat is developed in the dielectric material across portions of the width of the material corresponding to respective ones of the parts of the second electrode.

The electrodes need not be rollers they could be flat platesand if the pattern to be imprinted were to consist of straight lines running along the length of the material the raised portions could be provided for example by wheels or rollers, and the material could be fed by some other means.

It could of course be arranged that the large roller forming the first electrode was smooth and that each of the parts of the second electrode had a raised pattern on its surface and that these parts were geared together.

The thermoplastic dielectric material could be a single sheet of a particular material or a laminate consisting of a foamed plastics layer between two sheets of plastics material. In the latter case the pattern and the spacings of the rollers could be such that the two outer sheets and the foamed plastics layer were welded together in accordance with the raised pattern on the surface of the roller 1.

It is possible by making the length of each pressure roller between 13 to 20 inches and by using a separate one kilowatt generator at frequencies between 50 and 150 megacycles for each source to match adequately each of the loads provided between the pressure rollers and the roller 1 by plastics material such as polyesters, polyamides or acetates and to weld material of a total width of 40 to 60 inches.

The ability to use higher frequencies may be seen from the fact that for a weld of a particular width, for example one eighth of an inch wide, it is possible to use a frequency of 70 mc./s. over a length of twenty inches, however,'for a length of forty inches of the same width of frequency of 36 mc./s. may be necessary, and for a length of fifty inches it is necessary to use a frequency of 20 mc./s. The disadvantage of using a lower frequency is that it is necessary to increase the power to be supplied to the materialto obtain the same degree of heating. The voltage between the welding electrodes is also increased and the possibility, especially with thin materials, of a breakdown through the material is therefore increased.

The pressure rollers may of course be sleeves arranged on their respective shafts, and their positions on the shafts may-be made adjustable.

In order to avoid interference it may be arranged that each of the sources is at a different frequency.

Referring to FIGURE 3 there is shown an arrangement including a first electrode consisting of a roller 10 having a raised pattern on its surface and two pressure rollers 11 and 12 forming a second electrode. The rollers 11 and 12 are displaced around the periphery of the roller 10 but effectively cover a length of the roller 10 equal to the -width of a plastics material to be embossed.

Sources

13 and 14 of high frequency electrical power are connected respectively between rollers 11 and 1t and 12 and 10. The operation of this arrangement is similar to that described with reference to FIGURES l and 2. When plastics sheet material is passed between roller 10 and the pressure rollers as the result of a drive being applied to the roller 10 the material is embossed or in the case of a laminate material welded according to the raised pattern in two parts each extending across a part of the width and corresponding to the two parts of the second electrode.

With reference to FIGURE 4 an arrangement is shown in which there is a first electrode formed by roller 15 and a second electrode formed by pressure roller 16 connected at different points to sources of high frequency

electrical power

17 and 18. The other terminals of the sources are connected to roller 15. The connections are such that as a result of the loads presented the roller 16 is effectively divided into two parts with respect to each of the sources. Thus power from one of the sources is dissipated in the plastics material fed between the rollers at points corresponding to one of the parts while power from the other of the sources is caused to heat the material at points which correspond to the other of the parts.

It could be arranged for a single source to be used and for feed points from the source to be connected at intervals along the length of the roller 16 so that the roller was effectively divided electrically with respect to the high frequency source into a plurality of parts. Each of such parts is capable of being matched to a source of much higher frequency than it would be possible to use were the electrode to appear to the source to be a single roller, equal in length to the combined lengths of the parts and each of the parts causes heat to be developed in the material according to the electric field associated with it across a portion of the width of the material corresponding to the respective part.

In FIGURE an arrangement of rollersZt), 21 and 22 is shown which is similar to that described with reference to FIGURE 3. However, the connections from the source 23 are arranged so that power from the source is divided between the load provided by the plastics material passed between the rollers in two parts. Thus the power dissipated beneath electrode 21 heats one part of the width of the material and the power dissipated beneath electrode 22 heats a further portion of the width of the material.

Referring to FIGURE 6 there are shown four composite rollers having

electrode portions

25, 26, 27 and 28 and

portions

29, 30, 31 and 32 made of insulating material. The rollers are arranged in line and

electrode portions

25 and 27 have raised patterns on their surfaces.

A source 33 of high frequency electrical power is connected to

electrode portions

25 and 28 and in operation the rollers are geared together so that a sheet of plastics material may be fed in one direction between

electrodes

25 and 26 in the opposite direction between

electrodes

26 and 27 and back again in the original direction, between

electrodes

27 and 28. The electrodes form effectively the plats of a number of capacitors in series and the plastics material is the dielectric of the capacitor. It can be seen that both

electrodes

26 and 27 are effectively divided into two parts. One of the parts of electrode 26 co-operates With electrode 25 and the other part with electrode 27. The other part of electrode 27 co-operates with electrode 28. Thus both

electrodes

26 and 27 are divided into two parts so that power is developed as heat in the plastics material across a portion only of the width of the material corresponding to a respective one of the parts.

With reference to FIGURE 7 it can be seen that a first electrode formed by

rollers

35 and 36 is divided into two parts. The

rollers

35 and 36 are geared together and have a raised pattern on their surfaces. Pressure roller 37 forms the other electrode of the arrangement. High frequency electrical power from a source 39 is split, by the centre tap connection 40 made between the source and roller 32 and the

end connections

41 and 42 made between the source and

rollers

35 and 36, into two parts. The power developed in any plastics dielectric material passed between the electrodes is thus divided into two parts each extending across a portion only of the width of the material and corresponding to the division into two parts of the first electrode.

It has been found that use of the invention provides a better control of the heat generated across the width of a sheet of material than was possible previously, and that by the use of higher frequencies difiiculties caused by standing waves or other reasons are reduced.

Although the invention has been described in relation i to embossing and welding its use is not limited to these applications and it may be used for other purposes such as drying materials during a step in production.

It is of course necessary for maximum efiiciency for the loads presented by each of the parts of the electrode and its respective portion of material to be matched acourately to the source of power at the appropriate frequency so that the degree of heating may be properly controlled.

I claim:

1. A high-frequency dielectric heating process which includes the steps of supplying high frequency power from a source to two electrodes so that a high frequency electric field is set up between the electrodes, and passing a dielectric material in a longitudinal directi on'between the electrodes, the arrangement being such that one of the electrodes is effectively divided electrically with respect to the high frequency power into a plurality of parts arranged across the width of the material so that each part covers a, portion of the material not covered by another 3 part during the passage of the material between the. electrodes whereby power. from the source is developed as heat in the material across different portions of the width of the material each corresponding to a respective one of the said parts.

2. A process as claimed in parts of the electrodes are one another.

3. A process as claimed in claim 1 in which the said parts of the electrode are connected together electrically with respect to a direct current.

4. High frequency dielectric heating apparatus including a first electrode, a second electrode arranged to press a dielectric sheet material towards the first electrode, means to cause relative movement between the material and the electrodes, a source of high frequency electrical power, and electrical connections between the source and the electrodes, the arrangement being such that in operation one of the electrodes is effectively divided electrically with respect to high frequency power from the source into a plurality of parts arranged across the width of the material so that each part covers a portion of the material not covered by another part, whereby power from the source is developed as heat in the material across different portions of the width of the material each corresponding to a respective one of the said parts.

5. High frequency dielectric heating apparatus as claimed in claim 4 wherein one of the electrodes has portions of its surface raised.

6. High frequency dielectric heating apparatus claim 1 in which the said electrically insulated from References Cited UNITED STATES PATENTS 2,525,355 10/1950 Hoyler 219-1081 X 2,542,702 2/1951 Prow 219-10.81 X 2,616,015 10/1952 Kinn 219-1081 2,766,362 10/ 1956 Kinder et al 219-10.61 X

FOREIGN PATENTS 493,750 6/1953 Canada. 484,804 12/ 1953 Italy.

RICHARD M. WOOD, Primary Examiner. ANTHONY BARTIS, Examiner. L. H. BENDER, Assistant Examiner.

Claims

1. A HIGH-FREQUENCY DIELECTRIC HEATING PROCESS WHICH INCLUDES THE STEPS OF SUPPLYING HIGH FREQUENCY POWER FROM A SOURCE TO TWO ELECTRODE SO THAT A HIGH FREQUENCY ELECTRIC FIELD IS SET UP BETWEEN THE ELECTRODES, AND PASSING A DIELECTRIC MATERIAL IN A LONGITUDINAL DIRECTION BETWEEN THE ELECTRODES, THE ARRANGEMENT BEING SUCH THAT ONE OF THE ELECTRODES IS EFFECTIVELY DIVIDED ELECTRICALLY WITH RESPECT TO THE HIGH FREQUENCY POWER INTO A PLURALITY OF PARTS ARRANGED ACROSS THE WIDTH OF THE MATERIAL SO THAT EACH PART COVERS A PORTION OF THE MATERIAL NOT COVERED BY ANOTHER PART DURING THE PASSAGE OF THE MATERIAL BETWEEN THE ELECTRODES WHEREBY POWER FROM THE SOURCE IS DEVELOPED AS HEAT IN THE MATERIAL ACROSS DIFFERENT PORTIONS OF THE WIDTH OF THE MATERIAL EACH CORRESPONDING TO A RESPECTIVE ONE OF THE SAID PARTS.